Stubble - Managing the Resource

By Rohan Wardle
Research and Extension Agronomist

Please note that this is text only. To view the figures, photos and diagrams you will need to download the full document. (.pdf 1.4MB)

IT IS RECOMMENDED THAT YOU DOWNLOAD THE FULL DOCUMENT TO GET THE FULL VALUE OF THIS DOCUMENT WHICH IS MOSTLY PHOTOS AND DIAGRAMS. If you would prefer the hard copy to be posted to you please email your request to office@sfs.org.au

Rohan Wardle - National Landcare Research Project, initiated February 2005.


“Why Stubble Retention?”

  • h soil water infiltration & PAW holding capacities.
  • i surface (slaking) & subsoil (sodic) hostilities.
  • h Organic Carbon %.
  • i soil erosion potentials.
  • h land stewardship by not burning.
  • i soil bulk densities.
  • h energy supply to grazing animals.
  • i off-site leakage/loss of nutrients & pesticides.


Credible benefits, but how do we make them work?

“Some common approaches to Stubble Retention”
Incorporation / Destructive

High energy demands, with low Summer rainfall events tending to limit the rate of stubble decomposition

“Surface Retention of Stubble”
Time consuming, but effective!

“How about Grazing the energy reserves?”

Photo 1: Approx 8.5t/ha of Residue
Photo 2: Approx 4.5t/ha of Residue

Grazed with supplements:

  • Only a drop of half a condition score.
  • Residue knocked into furrows, requiring future management.

“Farmers out having a GO!”


“Why NOT Stubble Retention”


  • Blockages at seeding – toolbar design
  • Toxins released from stubbles with rainfall
  • h biodiversity…slugs, snails, mice, other pests?
  • Change in micro-climate
    • cooler, wetter conditions slowing germination
  • i N availability / immobilization – C:N
  • i efficacy of some residual herbicides
  • h severity of foliar diseases – YLS, Scald…


“Common Problems associated with Stubble Retention”

“Phytotoxic Liberation”
Canola following Wheat
Research (Bruce et.al; 2005) suggests that:

  • · Stubble retention can have a negative effect on plant establishment (up to 33%);
    • with varietal influence (based on the vinegar effect) being highly significant.
  • · Shoot biomass can be reduced by up to 30%.
  • · Overall grain yield can be reduced (up to 23%) with wheat stubble loads > 5-6t/Ha.


“Residue Managers can offer hope”
Inter-row suppression of common weeds

Photos: Current results at Lake Bolac and Mt Pollock


“Micro-Climatic Effects”
Canola following Wheat
Additional Research from Bruce (et.al; 2005) suggests that:

  • · Stubble retention ↓ surface soil temperatures by up to 3.8ºC, resulting in seedling deaths.
    • This effect may be worse in colder environments (especially the WD of Victoria), if crops are sown late.


“Nitrogen Tie-Up”

  • As stubbles decompose, soil N is tied-up by soil organisms that use it to break down the residue, thereby limiting N available to the crop:
    • More a problem (for cereals & canola) with dry Summers, followed by wet Autumns.
    • Consider extra N at sowing, or grow grain legumes after cereals.



“Cellulose Digesters”
Anecdotal evidence suggests that:

  • Urea + molasses + fulvic/humic acids + commercially available bacteria and biological products can significantly reduce stubble residue loads remaining on the surface.
  • Just incorporation can ferment the stubble, killing any soil microbes:
    • The addition of N & K can remedy this dilemma.
    • Current trial work with caustic soda shows promise.


“Machinery Requirements”

  • Deep toolbar – vertical & horizontal clearance:
    • Minimise any blockage / pinch points.
  • Residue managers / disc openers, tine & press wheel assemblies:
    • Capable of placing all seed & fertilizer in one pass with adjustable pressure for optimal seed-soil contact;
    • Depth control system dependant on press wheels.
    • Banding of N to prevent toxicities.


“Toolbar designs to maximise trash flow”
Photo: 2005 SFS Prototype
Photo: “Toolbar designs to maximise trash flow”
Photo: the StubbleStar more information -> http://www.weedscrc.org.au/projects/project_2_1_2_1.html



“Desired Outcomes”

No “ONE” solution

  • Everyone has a combination of differing strategies
    • Variety selection (short strawed)
    • N timing (canopy management)
    • Harvest distribution of residues
    • Stubble cut (200mm – 300mm) vs left standing
    • Post harvest incorporation vs seeding trafficability
    • Bale & remove vs microbial digestion
    • Inter-row skip seeding
    • Rotational Management
  • h Harvest Index
    • Grain yield ÷ total biomass


“Burning is the Current Non-Preferred Stubble Management Approach”

Proactive research will allow for its use as a strategic tool into the future!

“Increasing Incidence Of Glyphosate Resistance In Australia”
Graph: Number of resistant populations – year.


“Ryegrass Control With Burning”

Control is more effective if stubble is in windrows

Emergence of ryegrass after burning - % of untreated – windrow/standing

“Nutrients in Wheat Stubble”

  kg/t of stubble $/ha for 4t/ha of grain
(HI = 0.42)
Nitrogen 6 $33
Sulphur 0.8 $1
Potassium 44 $35
Phosphorus 0.8 $1
Carbon 400 ?????



“Current Scenarios”

  • First field visit – post sowing to review physical performances:
    • Field establishment
      • Slugs, RLEM, European earwigs, Lucerne Flea.
      • Economic feasibilities of individual approaches.
        • Long-term site benefits.


What works for you???

“Managing the Resource”
2005 Lake Bolac Trial Plan


“Stubble – the Future”

  • If managed correctly, stubble retention can be a useful weed management tool.
  • Every season will present an alternative approaches.
  • Burning is not the only tool available to manage crop stubbles.


Good Luck!!

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